Purification and recovery of acidic materials



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L.. U. FRANKLIN PURL'FICATION AND RECOVERY OF ACIDIC MATERIALS L/ea/lc'e (ZE/ank Zin y july 3l, 1951 Filed March '7, 1946 Patented July 31, 1951 .4.

UNITED-- STATES- PATENT ori-ICE IeslieU. Franklin, Port Arthur, Tex., assignor to Gulf Oil Corporation, Pittsburgh,` Pa., a corpo"- ration of Pennsylvania Appl-ication'March 175 This inventionrelates to thepuri'catiomand recovery of 'acidic materials. More; particularly,

the invention is concerned'Withaprocedureior.

the recovery of the.acidiccomponentsloi.sludgesf.

resulting from the treatment ofhydrocarbon mixtures. with acidic materials. andif'or` thepurifi'ca-rvr tion ofsulpliuric.acid.'v

Large quantities. of. acidic. mixtures containing acid .componenta commonlyl called acidsludges,`

are obtained from various. petroleum. treatment.` Thus, large quantities of Waste sul procedures. phuric acid inthe form ofracidsludgesare obtained as Va result of sulphuric acid catalyzed hy drocarbon .alkylaticnsA Such acidic. mixtures. are. composed.A predomif nantly of an. acidic. component,.e,. g.,su1ph.uric. acid, plus minor quantities` oilinorganic; or. or.r-

ganicmatterwhich serve tocontaminate and :di-

lute the activeingredi'ent. Generally, theseacidic.. mixtures, arenot suitable for. further use inthe treatment of'petroleum products, .but-.their active.v

acidic material may be utilized.. for furtherpe troleum treatment providedthat the.v active ma-V terial is separated and'. recovered from the conf taminating ingredients off. the.. acidic. sludges.

A.. principal objectoi. the. presentinventioir is the. provsionrof. a procedurefor thethe purificationandrecovery of. acidic materials14 A further.

objectli's thefprovisionof aprocess for. thevpuri-w iication of'acid sludges resulting irompetroleum treatment procedures. and for the-recovery of the acidic component of. these sludges in a high degree of' purity in an economicall and efcient manner. A still further object is the purication of. sulphuric acid sludges resulting from hydrocarbon alkylation procedures Whichwillyield the recovered sulphuric acid in a suiiicient degree of purification to permit its re-use in the alkylation process by a procedure which does not involve the expensive. steps of hydrolysis, concentration and fortification or the steps of complete oxidation of the acid sludge, gas purication, catalytic conversion and fortification,

Another object is the provision of. a simple, continuous process for the purication and recovery of sulphuric acid from acid sludges resulting from petroleum treatment procedures. A further object is the provision of a process for the removal of emulsion-forming impurities from impure sulphuric acid resulting from hydrocarbon alkylation procedures so as to decrease. the tendency of the sulphuric acid to'form difliculty resolvable-emulsions. Other objects and the entire scope of applicabiliti7 of this invention will become apparent from the detailed description givenhereinaiter;

1946, SeriaLNo, 652,704;A

(Cl. ,2S-172) These. objects. arey accomplished according toi the -process of the presentlinventionby contactV5 ing impure acidic. mixtures resultingl from, petroleum treatment'procedures with liquid ,sulphur dioxide under proper conditionsso. that theiin-.-

` purities inthe mixtures. are removed therefrom.

andthe acidic vor principal' con'iponen't.srcc'ovf-V ered in substantially pllreiorm. c The success ofithe pres'entinvention depends..` 1l), primarilyL upon the discovery tl'iatacidicsludges from petroleum treatment ptocedures,` andin. particular, sulphuric ,acid s1i1d`ges,may befre'ed. of their contaminating impurities'.byZ controlled.. extraction with liquid sulphur dioxide. 15.V It has beenfoundV that.sulphuric.acid.sludges, "such as those resultingcfrom'.hydrocarbon alkylaf.-` tion procedures, are. composed-.of sulibl-i'uric..-a'cid,.n sulphuric acid hydrates, :liquicllsulphur-dioxdesoluble impuritieswhich are apparently. soluble.. in sulphuric acid and are .characterizediby their.

ease of oxidation', red color and?A transparent sof-V lution, when dissolved in liquidgisul'piliurfdioxide,.A and liquid. sulphur'-dioxide-insoluble.,impurities which appear* to.exis't'.in.part. asasolutioniin the...v 2@ sulphuric acid and in partas a .colloidal suspen.r

sion in the acid and characterized by, theirbl'ack color, high viscosity. andlge'neral terry. appear.- ance. This invention further involves-the discovery thaty sulphuric. acid or...its hydrateslare 39so1uble to an appreciable. eXtentinWarm/liquid. Lsulphur dioxide, andrelativel'ygless4 solublefincold. liquid sulphurV dioxide.. Whilet the diierences` in respective solubilityI of' sulphuric acid and`.the.- contaminants of. the subjectacid sludges are 4suiii. l,ciently large to permit the, separation .ot-.theimf 'f `purities from the'. impure .sulphuric-acid.,. y Themanner; in which these discoveriesmau be utilized for purification of acidslud'ges maybe., briefly stated as. follows; The acid. sludge .t'o.,be 40 .treatedV is.contacted with liquidSOz=under.such= conditions that' the acidic componentof., the sludge is separatediromthe undesirable impuri.- I ties and the purified acidic'materialis recovered in substantially pure form. The ,contactingoi 45, the acid sludge with liquid.Sz-under.suitable;.

conditions may be effected by., two differenteenf.. eral series of operationallsteps'. f- In the rst of these. seriesofstepscr.schemes,

the acid sludgeis. contactedwitli liquid SO2 in -av countercurrent manner*y atl a temper'aturersuffi-u y ciently low, e: g., 20"FE, to permit tlieoasoluble,Y

impurities of the sludge to dissolve in theliquid SO2 Without'dissolvingany appreciable. `quantity i.

off Vsulphuric acidjor its hydrat'es., The liquidlSOza containing the dissolved impurities is.separated;-E from the't'reate'd acidslud'ge, subjected'to evaporation to remove the dissolved impurities therefrom, compressed, condensed and recycled to the sludge contacting step.

The acid sludge which has been treated at the low temperature with liquid sulphur dioxide is then contacted in countercurrent manner with another Yportion of liquid sulphur dioxide at a temperature which is suliciently high, e. g., 80 F., to dissolve substantially all of the sulphuric acid in the liquid SO2. This SO2 acid mixture is then separated from the insoluble impurities. Thereafter, the temperature of the SO2 acid solution is lowered to a temperature suiiiciently low, e. g., 20 F., to precipitate all the acid from the solution after which the precipitated acid is recovered, while the sulphur dioxide is recycled to the process step of contact at the elevated temperature with further partially treated sludgeY In the second scheme, .the acid sludge is first contacted with liquid sulphur dioxide in a countercurrent manner at a temperature suiciently high, e. g., 80 F., to insure the solution in the sulphur dioxide of substantially all of the acid, its hydrates and the SO2 soluble impurities, while the undissolved SO2 insoluble impurities are separated from the resulting Solution. The resulting solution of SO2 in acid is then cooled to a temperature sufficiently low, e. g'., 20 F., to precipitate the dissolved acid from the solution while retaining in solution substantially all of the SO2 soluble impurities. The precipitated acid is then contacted with further liquid sulphur dioxide in a countercurrent manner at a temperature suiciently low, e. g., 20 F., to dissolve any of the SO2 soluble impurities remaining in the acid Without dissolving any appreciable quantity of the acid. Finally, the purified acid is separated from the liquid sulphur dioxide. The separated sulphur dioxide is distilled, compressed, condensed and recycled to the process for further contact at the indicated low temperature with further partially treated sludge.

For a more complete understanding of the process of this invention, reference is made to the attached drawings, in which Figure 1 is a diagrammatic view of apparatus suitable for use in conducting the first series of steps, scheme I, described above; and

Figure 2 is a diagrammatic view of apparatus suitable for conducting the second series of steps, scheme II, described above.

Referring in detail to the drawings, there is illustrated in Figure 1 a packed tower 2, provided With a uid inlet line 4, a fluid outlet line 6, a`1iquid SO2 inlet line 8, and a liquid SO2 solution outlet line I0. In this packed tower 2, the raw acid sludge to be treated is introduced through line 4 and caused to countercurrently contact recycled liquid SO2 at a temperature of, for example 20 F., and a pressure of 20 pounds abs., passing up through the column from the inlet line 8 to the outlet line I0.

A second packed tower I2 is connected to the tower 2 by the fluid line 6, which line is provided with a pump I4. This second tower I2 is further provided with outlet lines I6 and I 8, and inlet line 20. In addition, the top of the tower is provided with heat exchange coils 22, which are connected to permit liquid from line 24 or line 26 to be circulated therein and exit through line 28.

The partially treated sludge from tower 2 passes to the tower I2 through line 6 under the action of pump I4. In the packed tower I2, this partially treated sludge is caused to Contact all elevated temperature and pressure, for example F., and 65 pounds abs., recycled and distilled liquid SO2 entering through line 20 and passing upward through the tower and out the exit line I8. As a result, substantially all of the sulphuric acid in the partially treated sludge entering the tower I2 through line 6 is dissolved in the liquid SO2 passing through the tower I2 from inlet line 20. The resulting solution of the sulphuric acid in liquid SO2 leaves the tower through the exit line I8, while the impurities from the acid sludge, which are insoluble in liquid SO2, are separated and removed from the tower through line I 6.

The exit line I 6 of the tower I2 connects to a stripper 30 which is provided with exit lines 32 and 34. In the stripper the SO2 insoluble impurities are separated from any dissolved liquid SO2 by heating the materials therein. The stripped SO2 insoluble materials are removed from the stripper through line 32, while the separated sulphur dioxide is removed as gas from the stripper through the gas line 34 and is eventually purified and recycled as is described later.

The SO2/acid solution leaving tower I2 through line I8 passes to the heat exchanger 36 and then to the acid settling tank 38. This acid settling tank 38 is provided with exit fluid lines 40 and 42, the line 40 serving to remove liquid SO2 from the tank and line 42 serving to conduct acid from the tank.

In passing through the heat exchanger 36, the SO2/acid solution which leaves the tower I2 at a temperature of about 60 F. is further cooled to a temperature to about 15 to 20 F. Thus, this SO2/acid mixture enters the acid settler 38 at a temperature of about 15 to 20 F. and a pressure of about 60 pounds abs. The reduction of temperature from that prevailing in the tower I2 to that in the settling tank 38 causes the acid dissolved in the solution to precipitate. The precipitated acid is removed from the settling tank through line 42, conducted to a stripper and finally conveyed to storage or is recycled to the petroleum treatment procedure. The supernatant liquid sulphur dioxide is removed from the acid settling tank through the line 40 under the action of pump 44 which recycles the supernatant SO2 back to tower 2 through the line 8 into which line 40 connects.

The contact of the fresh acid sludge with liq-l uid SO2 in tower 2 at the indicated conditions resuits in the formation of a SO2 solution of SO2 soluble impurities from the acid sludge. This solution leaves the tower 2 through exit line I0 at a temperature of about 20 F., the major portion of this solution is conducted through line I0 to the heat exchanger 36, but a minor portion of the solution is by-passed through line 24 to the cooling coils 22 and then re-enters the main line IU through the cooling coil return line 28. Thus, the cold solution by-passed through the cooling coils serves to cool the SO2/acid solution exiting from the tower I2 through the line I8, as described above.

The solution passing from the tower 2 through lin-e I0 enters the heat exchanger 3B at a lower pressure than that prevailingI in the tower 2, e. g., 10 pounds abs. As a result of the low prevailing pressure, the sulphur dioxide in the solution is vaporized with the absorption of heat. |This vaporization results in the production of SO2 vapors which leave the heat exchanger through line 46 and unvaporized SO2 soluble impurities which leave the heat. exchanger through iiuid line 48.

.TheSOz vapors lpass ;-through..1ine 45,120 the compressor 5t, where they .are 4coimoressed and liquefied and4 recycled to the heat-,exchanger 35 through line 52. Herea portion of theheatof compression is removedv and the lioueed-.sulphur dioxide is then conducted tothe tower l2 .through the line Zitto whichline `52 connects. Line .2is provided vwith bypass line Y2t which indirectly connects line ,25 toline il] through Ycoils 42.2 and line 2.8. This by-,passliner 25. permits-acontrolled amount .of distilled liquid SO2 to be charged .to line. loin order to maintain the necessary material balances between the separate stages ci the process.

The unvaporized SO2 soluble impurities pass from the exchanger .35throughline-.d8 to a stripper '54. .In this stripper 4the unvaporizediimpurities are separated from any dissolved ,SQz by heating the mixture to atemperaturetofyahout 80F. The sulphur dioxide vapors-strippedlfrom the impurities pass out of the stripper through line 55 which connects ,to line Srl-leading from stripper 3G. The stripped impurities Vexit from the stripper 5d through the removal line eiland,

areconducted tostorageor waste. Similarly, the settled acid whichisremoved from the-settling tank 3,8 through line i2 ispassedthrougha--stripper '50, wherein vany sulphur dioxide dissolvedin the settled acid is removed byheating the acid to a` temperature of; about 80aF. Any SO2 vaporized in` stripper i is removed from kthe stripper through the exit line E52 which connects with line 3d and which, in turn, runs to the compressor 64. The stripped acid is removed; from the stripper through line S6 and isconductedfto storage or recycled for petroleum product treatment.

The SO2 vapors obtainedfromfstrippers tutes and EEB through linestii, 56 and V62.enter acompressor S4 where they arecompressed-.andliquefied. The liqueled SO2 leaveszthe compressor :64 through line $3 whichsplitsinto lines "mand 1.2, the line 'i9 connecting to line. for'conductionfof liquid SO2 tortower 2, while the line l2 connects to line. 52 for passage of liquidfSO'zzthroughsheat exchanger 36 and-then into line;v 2li for: entrance into tower i 2.

Figure 2 illustrates a form of apparatus which is useful in carrying out the second schemeof steps as indicated aboveiorpurication of acid sludges. This drawing shows a tower L82 provided with iluid inlet lines [t4 and |86 and fluid outlet lines lilS and lli). The topof the tower is also provided with cooling coils H2 connected. to the cooling coil inlet line lili .and the cooling coil outlet line lil. The towerV |02 is operatedat a temperature suiciently' high, e. g., 80 ligand a corresponding pressure, e. g, 65-,pounds alosuto insure the solution of substantially allor" the acid sludge .entering the tower through' the 4acidsludge charge line ltd in the liquid SO2 passing up through the tower from thein'let line |96, The countercurrent Contact of the acid sludge-charge with the sulphurdioxide `in tower M32 results in thefformation of a solution of the acidin'suphur dioxide. This SO2/acidsolutionleaves the; tower through outlet line ISB. .At thee-ame time,..the impurities of the acidV sludge, whichgareinsoluble in liquid SO2, pass downward through the tower and are removed therefrom through outlet line H0. rihe insoluble 4impuritiesare conveyed by line llt to stripper. I8, where-.any SOzdissolved in the resulting SO2.insolubleimpurities -is.removed therefromiby reduction .ofgpress-ure upon the mixture. This strippingA procedure resultsin the separation of SO2 insoluble sludge impurities free from SQz'whichleaves Vthe stripper through exit.l line i--:and SQmgfaswwhich leaves the stripper` through gasline |22. `The impuritiesare conveyedby line |20 lto .storageor waste, while lthe SO2 .vapors are'conveyed by line ,lf2-2 to .a com= pressor unit` and :recycled in the system, as ex= plainedmore. fully below.

fAs indicatedabove, thetowerltz is preferably operated -at-a temperatureofthe order .of 86 andra .pressureeoithezordergof 65 poundsabsolute. ThrOugh theiaction ,ofthe-,cooling coils IfZfIJ,y the solution of ,SQz ,in acdleaving the tower I QZ through ,duid line Hi8 Vis cooled ,to a temperature of preferably ;60 F. AThis partially cooled. solutioniiszthen vconveyed throught-he fluidv line Hi8 to heat exchanger |214, wherelfurther *heat; is, re moveclfromr thefsoluticnand its temperature `reduced topreferably aboutl5fto20 l. vThem-ixN ture in this cool state is then conductedbyzfiud line |26 togan acid;settling tank |28. Asa result of :the reductionof thevtemperature of thefsolution of VSO2intacid,.theacidin `thesOIutiOnls preu cipitated. The precipitated acid settles ,to the bottom of theacidsettlirlgztani; andis removed therefrom throughY line loo, while the supernatant liquidA SO2 is decanted iromtheesettling tank through line |32. Thedecantedsz is conveyed by the line |32 under the action of pump is@ through heat .exchanger l t :whichserves toy heat the liquid,thence throughLline |38 :to heat exchanger Itufwhere the liquid sulphur dioxide becomesiurther heated, ,andgisl nallyl returned .to the tower |102 through thepuidline {G6-.connecting the exchanger ill 01 .withvv the 'tower |y 02.

The-settled,partially .treated zacicl` issuing from the settling `tank |28;isconveyed by the fluid line |39 to the packed tower` |42. This tower ispro vided, in additionto .theinletjline |3 |l,with inlet line Maud outlet lines I 46;;and |48.

The tower |42 is ,operated at a temperature suiciently lowso that ktheliquid SO2 passing countercurrently upward throughv the tower .from inlet .M4 to outlet line |46 dissolves substantially noneof the partially treated acid sludge passing countercurrently downward through the tower frominletlinedto outlet line ist, e. g., aitemperature .of theorder of 20 F. and acorresponding pressure -of the` order of 20 pounds abs.

lIll-1e,.countercurrent contact of partially treated sludgeA and. liquidfaSQz, .at the conditions existing in tower 4.2, results1.inthe production of puriied acid which leavesgthegtowerV through exit line Hi8 andfa solution .ofsSOzzsoluble .sludge impurities in liquidrSOz :which leaves the towerthrough theA exitline |46. ,Thepuriedfacid-isrconveyed by theline let-to a stripper |250 wherein anysulphur dioxide dissolved in the treated -acid is removed asvaporgby.theapplicationof heat to the treated acid. The SOzgfreesacid is removed from the stripper through the fluid line `|752 and lis conveyed to storage or is recycled-in'further petroleum product treatment. 'The gaseous sulphur dioxide is removed vfrom the stripper throughthe vaponline |5l which connects'to the vaporline The `solution 'of-SO2 vsoluble sludge impurities issuing -irom- 4the atop., of l tower |42 through rthe line .of |45 is @splitf in two 'portions by rmeans `vof valve., |56. i One `of rthese portions passes-'through the -line |41 to .the cooling coil ||`2 where this cold solution serves to remove heat from the SO2/acid solution leaving tower |02, as -is `describedabove YThersol-utionfthen passes-through returnline. ||6 where it is combined-with the remainder; of..the:so1ution1and conveyed through the fluid line |58 to the heat exchanger I 24. The heat exchanger |24 is operated so that the solution of SO2 soluble impurities from tower |42 is maintained under a pressure of 10 pounds abs., while this solution is heated in the heat exchanger |24. As a result of this heat increase and pressure reduction, the sulphur dioxide in the solution is vaporized and separated from the unvaporized impurities as gaseous SO2 through the vapor line |60. The unvaporized impurities are removed from the heat exchanger through the fluid line |62 and are conveyed to a stripper |64. In the stripper any SO2 dissolved in the separated impurities is removed by vaporizing the sulphur dioxide. The vaporized sulphur dioxide is removed from the stripper through vapor line |66, while the sulphur dioxide free impurities are conveyed through the exit line |88 to storage or waste.

The SO2 vapors generated in the heat exchanger |24 are conveyed by the vapor line |60 to a compressor |10 where they are compressed. The SO2 vapors generated in the strippers V| I8, |50 and |64 are also compressed in a compressor |12. The compressed SO2 from compressor |10 fows through fluid line |14 which joins with the uid line |10 conducting the compressed SO2 from compressor |12 to form the common fluid line |18 which conveys the combined streams of compressed sulphur dioxide to the heat exchanger |40. In the heat exchanger |40, a portion of the heat of compression is removed and the partially cooled liquid SO2 is conveyed by line |80 to heat exchanger |24 where a further portion of the heat in the liqueed sulphurl dioxide is removed. The cooled sulphur dioxide is then conveyed through the fluid line |44 under the action of pump |82 to the tower |42. The fluid line |80 is provided with a by-pass line |84 which permits a portion of the liquid sulphur dioxide from heat exchanger |4 to be by-passed around the heat exchanger |24, so that the final temperature of liquid sulphur dioxide conveyed to tower |42 may be accordingly controlled. Fluid line |44 is provided with a by-pass line |86 which permits a portion of the distilled SO2 from the compressors to be combined with the SO2 soluble impurities solution leaving tower |42 by line |46 in order to maintain the proper material balance in the separate stages of the process.

Apparatus for conduct of the present invention is illustrated in simplified form by Figures 1 and 2 and it will be understood that conventional automatic or manually controlled means may be employed for regulating and controlling rates of flow, pressures, and temperatures throughout the process. In particular, flow controllers, pressure controllers, and exchanger by-pass lines have not been shown in the interest of simplicity.

In one respect, it may be considered that the order of procedure for the extraction steps is reversed in the two schemes, that is, in scheme I, the first stage is conducted at low temperature to extract soluble impurities only, leaving the higher temperature second stage to separate the dissolved acid from the insoluble impurities, while in scheme II the first stage is conducted at a higher temperature to separate all SO2 solubles (acid and impurities) from the insolubles, leaving the function of separating acid from soluble impurities to the steps conducted at low temperatures.

However, another difference in the two schemes is the purity of SO2 contacted with the acid sludge in the separate process stages. In scheme I, the'low temperature, first stage is charged with per cent recycle SO2 from the acid settler which has been once distilled since contacting SO2 soluble impurities, but has not been distilled after precipitating the insolubles in the high temperature stage. The first stage (high temperature) of scheme II is charged with 100 per cent recycle SO2 from the same stage after precipitating the treated acid in the settler. It is, therefore, substantially saturated with SO2 soluble impurities at all times, the excess of these impurities being drawn out of tower |02 with the insolubles.

The second stage (high temperature) of scheme I is charged with a mixture of distilled SO2 and clean recycle SO2 from the first stage and settler. In scheme II, the second stage (low temperature) is charged with distilled SO2.

Some minor exceptions to the above described purity of the respective SO2 streams may be seen on the detailed now diagrams, Figures l and 2, where necessary volume adjustments are made by transferring SO2 between the respective stages.

Another difference between schemes I and II is the nal source of treated acid. In scheme I, this acid is precipitated in the settler from an SO2 stream that has been previously purified from SO2 soluble impurities by countercurrent extraction in tower 2, followed by distillation. In scheme II, the treated acid is recovered by countercurrent extraction with distilled SO2 in tower |42.

Still another difference in schemes I and II f is the amount of compressor capacity required.

Using the respective typical temperatures and pressures described for illustration, scheme I requires compression of SO2 vapor from l0 lb./sq. in. absolute to 65 lb./sq. in. absolute pressure, whereas scheme II requires compression from l0 lbs. to some value less than 20 lbs. depending on the suction pressure of pump |82.

A further understanding of this invention may be had from the following illustrative examples in which all parts are by weight:

EXAMPLE I This example illustrates the purification of acid sludge, obtained as a product of a hydrocarbon alkylation, under conditions designed to handle a large volume of acid sludge per unit time with a relatively low degree of purication per pass.

The acid sludge from a hydrocarbon alkylation having the following composition:

Specific gravity, 60/60 F 1.75 Analysis: Wt. per cent:

H2804 equiv. to titratable acidity- 88 H2504 equiv. to acidity of completely oxidized sample 92 Carbon content 5.3

is treated in an apparatus of the type illustrated in Figure l and described above. The conditions of operation in the various steps of the treatment and the analysis of the products obtained are delineated in the table below.

EXAMPLE II This example illustrates the treatment of acid sludge under conditions designed to purify a large volume of acid per unit time at a relatively low degree of purification per pass by another series of steps than those employed in Example I.

LA'cidsludge oi' theanalysis indicated 'infExample I-I 'is 4treated `by kthe series of 'steps of scheme "II, described above, using the 'apparatus illustrated in^Figure 2. v"Iheconditionsof Yoperation of 4the apparatus-in the 4process Yas Well as the results 'and analysis Ain the productionsrobtained in the treatment `aredelineateddn .the table below:

Table .Example Example 'I `II Operating Conditions:

Liq. Vol. Ratioof SO2 to Ac1d Charge l First Stage'Tower 25 7 00 f Secon'd'Stage Tower 700 '10 Temperature, F.-

n FirstIStagev Tower (Top) 20 60 First Stage Tower (Bottom) 2O -80 Second vStage Tower (Top) ,-60 .-20 "Second Stage'ToWer (Bottom 80 20 .Acid Settler T20 20 Product Strippers 80 80 "Pressure: 13h/Sq. In. Absolute (Approx.)-

.First Stage 'Power 20 -65 Second Stage' Tower. 65 `20 -Acid.Settler F60 60 Evaporator-Exchanger. l l0 `Product Strippers '7 '7 -Sample 90 .Carbon Content l0 .TreatedAcid- `Yield,Wt. Per Cent of Gharge '90 -Specific Gravity, 60/60 E ,1.76

. Analysis, Wt., Per Cent:

-HSOl-Equiv-to Titratable Acidity 90 HQSOrEquivsto/Acidity of OompletelyzOxidized 93 vv'Iherequired ratios o'ijliquidSOz circulated to acid sludge chargedin theprocess,dependlinpart ori-the'type or" acid s1udge charged and the .temperatures selectedas being .best suited jforthe degree of purification desired. For example, some acid sludgesV willA contain a larger propo1- tion of SO2 soluble impurities than other acid sludges, possessingdiiierent solubilities in .liquid SO2, thus vrequiring different ratios oiSOztoacid sludge to insure complete solution of these ,irnpui-ities. Apparently'acid sludges obtained from severe treating. of lubricatingoils usually require higher ratios of SOato sludge" charged .thanacid sludges obtained 'fromJacid alkylation of butenes with isobutane.

` While thepresentV process 'may `be used ier. the treatment of generally all acidic sludgesthe process appears to be .especially useful `forpurifying alkylation Yacid sludges, and theillustratioiis vof quantities and 'qualities given 'herein willrserve to show lapproximations of what'may be exilectedby the process on this type of acid sludge. It.`should lieinoted that sulphuric 'acid alkylationprocesses normally-operate-with a system acidity '(titratable strength) 'of -85 wt. lpercent to 90mmpercent and 4that Yto A-maintain this acidity during alkylatiom `the vfresh acid used as make-'uprmustY be appreciably stronger thanithe system acidity. `If ^the Vmajor portion of thisvhigher strength make-up acidis -to be provided by continually or intermittently transferring a portion -of 'the jalkyla'tion acidsludgeffrom the alkylationsystem tothesub# 10 :lect process, operatedacoordingtoLscliemesflror II, for some 'degree of puriiicationrabovelits i normal lalkylation strength, and then to Jbe -retu-rned to -the alkylation systemfor make-up acidity, thenit is -obvious thatthe greaterthisplegreeof purication'achie'ved;theiessrwill be -the quantity of transfer A'acid required per unit io'f ltime "to "and Vii'omrthe subject process. Itis-equally trueltha't the' higher "the Vdegree of purica'tion'required "by 4the subj ect fprocess, 'the:greaterwillbe'tm"number of extraction stages required 1in each'st'ower and the higher'will-be the-ratio of`^$2 to a'ci'din -each-tower. A'Otheriactors suchjasitemperatures and time loffsettlingWill also"be"jaiectd by` the degree'of purification desired. 'f

lHenceyit is necessary, HVfrom an economicyie'w point, 'to 'Weigh" the 4advantagesy of Ta) `liandling'fa larger 'Volume of alkylatio'nacid sludge-charge per unit 'of' time inthe 'subject process andfprocessingwith' a lower degree ofjlouriiication against (b) handling a smallervolum'eofalkyla'tiomacid sludge charge with a higher degree of purication which entails, among other things a higher ratio 'ftSOz to yacid inthe extraction steps. Examples 'Land II-'above illustrate 'the former type of ,operation.

Itis apparent from f the 'discussion 'given above, thatvarious temperatures may be employed in thestep of contacting the acid sludge with liquid SOzfso asjto `dissolve tthe acid 'contained `in the sludge in theiSOz. This temperature should beas -highas possible. However, itthasbeen'foundde- 4sirablethatthe-maximum operating-temperature vshould be '100 F. Aor'belovv,y i-nvievv of theten'dency of the acid sludgesto decomposeiairlyrap- 'idlyinthe'presence of Vliquid SO2 at vtenriperatures above this iigure. Maximum operating temperaturesicetvveen 7 05F. `and`10,0 F; havebeen found tobeprefera-ble.

Y*',Similarlyfit Willibe-apparent that various temperatures 'may be employed for contacting 'the acid sludgewithiliquid sulphur 'dioxideso as 'to dissolve fthe VSO2 soluble impurities from the sludge WithoutV dissolving any appreciable 'quantity'i-ofacid. It is desirable` for a maximum. efflvciency 'ofthe'A process to employ as 'low atemperature as'possible inthe step. However, inview of the `tendency of` acid `sludges V,to 'solidify v inthe presence of liquid sulphur dioxide'vat temperatures below about '15 it' .is fd'esir'able to limit the minimum operating temperature 'to this rfigure. -A minimumoperating"temperature between 15 F. and-30 has beenlfound tobe .pre`ferable.

The pressures employedin' the' .various Steps Yof nay-recovery andl puricationprocess depend primarily upon the 'temperatures employed in the procedure and upon the', particular stage .in the process. "Where "liquid sulphur dioxide is necessary "in'the procedure, a pressure -suici'ent to maintain the sulphur dioxidel in the' liquidphase at the *prevailing temperature lis employed. '.On the other'hand, whereitis Ynecessary to vaporize the ,sulphur'dioxida a pressure lis employed `at which the sulphurdioxide will ex'it.in the vapor phase'under the prevailing temperature.

It has beenfound possible toincrease .the eaiseaeoe the conversion of a portion of the sulphuric acid to Water and sulphur dioxide. Consequently, the extent of use of oxidation as pretreatment of the acid sludge Will depend in part upon the ultimate purity desired in the purified acid and will be dictated by the economics of the process.

It has been found possible to increase the solu-` bility of the SO2 soluble impurities of the acid sludge in the liquid SO2 by the addition of various solvents in minor proportions to the liquid SO2. Benzene, ethyl ether and isopropyl ether are examples of such suitable promoters.

Various materials of construction resistant to the action of liquid sulphur dioxide and sulphuric acid may be employed for the construction of suitable apparatus for the subject process. However, since iron is the most economical material for this purpose, it is to be preferred in view of the fact that substantially no corrosion of iron processing equipment appears to take place in the operation of this process.

The subject purification procedure appears to be generally applicable to all acid sludges resulting from petroleum treatment procedures, although the process is particularly eicient in the purification of sulphuric acid sludges obtained in the alkylation of hydrocarbons. Any acid sludge to be treated by the process should be substantially free from entrained oils, particularly light hydrocarbons, in order to prevent the necessity of frequently purifying the process sulphur dioxide from the oils, since an accumulation of these materials in the sulphur dioxide appears to reduce the solvent power of the sulphur dioxide for the acid.

Local overheating and high isolated temperature in contact with used solvent or any of the products of my process should be avoided at all times, since the acid impurities are readily decomposed by excessive heat with the formation of undesirable water and coke. In connection with the presence of water in the process system, the presence of this material is harmful to the extent that it reduces the concentration of the acidity of the purified acid. For this reason, it has been found desirable to remove all oxide scale from the process equipment prior to the starting of the operation. This can be readily accomplished by the use of a warm 2 per cent aqueous phosphoric acid solution or a warm solution of 65 per cent sulphuric acid.

Small quantities of sulphur dioxide remain dissolved in the three-end products of my process and it is desirable to remove these last traces of dissolved sulphur dioxide. The use of strippers for this purpose has been indicated above and it has been found that a temperature of 80 F. and an absolute pressure of inches of mercury may be successfully employed in the stripping operation.

A distinct advantage of my process resides in the eiiiciency of heat transfer and low heat requirements associated with the process. The apparatus described above and illustrated in Figures 1 and 2 has been designed to utilize this feature to the maximum. It has been found that the only refrigeration required by the process is that which is needed to overcome heat absorption by radiation and mechanical heat imparted by the pumps and compressors. Apparently, there is no appreciable amount of heat liberated during the steps of contact of acid sludge with liquid sulphur dioxide.

The majority of the discussion above has been concerned with the treatment of sulphuric acid sludges. However, the procedure is also applicable to other acid sludges resulting from petrolum treatment procedures. An example of another type of acidic sludge which may be treated is aluminum chloride sludges. In the treatment of such mixtures, some minor modifications to the general procedure are desirable, such as the addition of small quantities of petroleum naphtha to the sulphur dioxide used in the process in order to facilitate the precipitation of the complexes of aluminum chloride and SO2 without requiring the use of abnormally low temperatures.

The present procedure provides an efficient and economical method for the purification of acidic sludges resulting from petroleum treatment procedures. The process is particularly useful in the treatment of sulphuric acid sludges, especially those resulting from hydrocarbon alkylations so as to purify the acid to a sufficient degree for recycle and re-use in the particular petroleum procedure. In addition, the method produces valuable by-product chemicals from the recovered SO2 soluble and insoluble impurities produced during operation of the process. If it is not desired to recover the by-product chemicals from these materials, they may be hydrolyzed in any suitable fashion to recover any small amounts of sulphuric acid which they may contain.

What I claim is:

1. The process for the purification of acid which has previously been contacted with hydrocarbons and which is contaminated with some resultant reaction products soluble in sulfur-dioxide and some resultant reaction products not soluble in sulfur-dioxide, which comprises contacting liquid sulphur dioxide with the contaminated acid at a temperature below 30 F. in such proportions that no substantial quantity of the sulphuric acid is dissolved in the sulphur dioxide, further contacting said sulphuric acid with another portion of liquid sulphur dioxide at a temperature above 70 F. in such proportions that substantially all of the acid is dissolved in said sulphur dioxide, separating the resulting solution from the undissolved components of the impure acid, decreasing the temperature of the sulphur dioxide solution to a value below 30 F., separating the sulphuric acid precipitated from the solution by the cooling operation and recovering the separated acid.

2. The process for the purification of sulphuric acid which has previously been contacted with hydrocarbons and which is contaminated with some resultant reaction products soluble in sulfur-dioxide and some resultant reaction products not soluble in sulfur-dioxide, which comprises dissolving the contaminated acid in liquid sulphur dioxide of a temperature above 70 F., separating the resulting solution from the undissolved components of the impure acid, cooling the separated solutionl to a temperature below 30 F. t0 precipitate the sulphuric acid therefrom, separating the precipitated acid from the sulphur dioxide and recovering the separated, purified sulphuric acid.

3. The process for the purification of sulfuric acid which has previously been contacted with hydrocarbons and which contains some reaction products soluble in sulfur-dioxide and some reaction products not soluble in sulfur dioxide which comprises extracting sulfur-dioxide-soluble reaction products from the sulfuric acid with sulfur dioxide at a temperature not substantially above 20 F.; separating the sulfur-dioxide extractant and its charge of sulfur-dioxide-solll- 13 ble reaction products from the extracted sulfuric acid; evaporating the sulfur-dioxide extractant, thereby recovering the sulfur-dioxide and separately obtaining the sulfur-dioxide-soluble reaction products; extracting the sulfuric acid a second time with sulfur dioxide at a temperature not substantially below 70 F., thereby effecting substantially complete solution of the sulfuric acid in the sulfur-dioxide while not dissolving the remaining reaction products present in the sulfuric acid; separating the solution of sulfuric acid and sulfur-dioxide from the undissolved reaction products, thereby separately obtaining the sulfur-dioxide-insoluble reaction products; and evaporating the sulfur-dioxide from the sulfuric acid, thereby recovering the sulfur-dioxide and separately obtaining purified sulfuric acid.

4. The process for the purification of sulfuric acid which has previously been contacted with hydrocarbons and which acid contains some reaction products soluble in sulfur-dioxide and some reaction products not soluble in sulfurdioxide which comprises: extracting the sulfuric acid with sulfur-dioxide at a temperature not substantially below 70 F. to effect substantially complete solution of the sulfuric acid and such reaction products present therein as are soluble in sulfur-dioxide, while not dissolving all impurities of the sulfuric acid; separating the solution of sulfuric acid and sulfur-dioxide and sulfur-dioxide-soluble reaction products from the undissolved reaction products, thereby separately obtaining the sulfur-dioxide insoluble reaction products; lowering the temperature of the solution of sulfuric acid and sulfur-dioxide and sulfur-dioxide-soluble reaction products to a temperature of the order of 20 F. or lower and thereby precipitating the sulfuric acid and most of the reaction products from the sulfur-dioxide; subjecting the precipitated sulfuric acid and impurities toa second extraction with redistilled sulfur-dioxide at a temperature of the order of 20 F. or lower to further extract the sulfur-dioxidesoluble impurities from the sulfuric acid; and settling the sulfuric acid from the sulfur-dioxide and sulfur-dioxide-soluble impurities, and thereby separately obtaining the puried sulfuric acid; and evaporating the sulfur-dioxide extractant, thereby recovering the sulfur-dioxide and separately obtaining the sulfur-dioxide-soluble imurities. p LESLIE U. FRANKLIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 911,553 Edeleanu Feb. 2, 1909 1,409,590 Salathe Mar. 14, 1922 Certificate of Correction Patent No. 2,562,608 July 31, 1951 LESLIE U. FRANKLIN It is hereby certiied that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 1, line 52, for difficulty read dz'cu-ltly; column 5, line 64, for suphur read sulphur; column 12, line 30, after of insert sulphwio;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oilice.

Signed and sealed this 2nd day of October, A. D. 1951.

THOMAS F. MURPHY,

Assistant ommisszoner of Patents. 

4. THE PROCESS FOR THE PURIFICATION OF SULFURIC ACID WHICH HAS PREVIOUSLY BEEN CONTACTED WITH HYDROCARBONS AND WHICH ACID CONTAINS SOME REACTION PRODUCTS SOLUBLE IN SULFUR-DIOXIDE AND SOME REACTION PRODUCTS NOT SOLUBLE IN SULFURDIOXIDE WHICH COMPRISES: EXTRACTING THE SULFURIC ACID WITH SULFUR-DIOXIDE AT A TEMPERTURE NOT SUBSTANTIALLY BELOW 70* F. TO EFFECT SUBSTANTIALLY COMPLETE SOLUTION OF THE SULFURIC ACID AND SUCH REACTION PRODUCTS PRESENT THEREIN AS ARE SOLUBLE IN SULFUR-DIOXIDE, WHILE NOT DISSOLVING ALL IMPURITIES OF THE SULFURIC ACID; SEPARATING THE SOLUTION OF SULFURIC ACID AND SULFUR-DIOXIDE AND SULFUR-DIOXIDE-SOLUBLE REACTION PRODUCTS FROM THE UNDISSOLVED REACTION PRODUCTS, THEREBY SEPARATELY OBTAINING THE SULFUR-DIOXIDE INSOLUBLE REACTION PRODUCTS; LOWERING THE TEMPERATURE OF THE SOLUTION OF SULFURIC ACID AND SULFUR-DIOXIDE AND SUL- 